The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Vehicles include power brakes with a brake booster. The brake booster amplifies brake pedal effort and applies the amplified effort to a master cylinder of a brake hydraulic system. The brake booster is powered by vacuum from the engine.
In addition to the brake booster, some vehicles also include a catalyst that treats an exhaust gas stream. Engine airflow requirements for warming the catalyst can reduce the vacuum that is available to the brake booster. When cold starting the engine, an engine control system may retard an ignition angle of the engine to increase the exhaust gas temperature. The increased exhaust gas temperature reduces the time needed for warming the catalyst to a catalyst light-off temperature. While the ignition angle is retarded, the engine control system may also increase the throttle opening to compensate for engine torque that is lost due to the retarded spark angle. The open throttle reduces the amount of vacuum and consequently reduces the amount of brake boost that is available from the brake boost assembly. This situation may increase braking effort for the driver while the catalyst is being warmed.